Neutral aqueous solutions of sodium fluoride were first used in the prevention of dental caries about 40 years ago. The initial clinical studies using neutral sodium fluoride were carried out by Knutson and Armstrong.sup.(1) and by Bibby.sup.(2). In the early 1960's, acidulated phosphate fluoride ("APF") appeared to be a preferred material in that some laboratory tests by Brudevald et al..sup.(3) indicated that the APF System gave a higher fluoride uptake than neutral sodium fluoride. Therefore, the predominant fluoride material used by dentists, hygienists, and other dental technicians since then has been the APF material. In the late 1960's, the APF material was introduced in the form of a gel. One such formulation is described by Elbreder in U.S. Pat. No. 3,337,412. Another APF gel is described by Weitzman et al., in U.S. Pat. No. 4,267,167. FNT (1) Public Health Rep. 58, 1701 (1943). FNT (2) J. Am. Dent. Assoc. 31, 317 (1944). FNT (3) Arch. Oral Biol. 8, 167 (1963).
Until this invention was made, as far as is known to the inventor the only pre-mixed fluoride gel intended for use by dental professionals that has been available commercially has been the APF gel. There have been disclosures in the literature of certain neutral sodium fluoride gels that apparently were either mixed by the user or by the investigator. For instance, see JASPD January-February 1975, 17-21, 36-45 (especially pages 38 and 40) (anon) "Everything You Always Wanted To Know About Fluoride Therapy", and references cited therein, especially: Englander et al., J. Am. Dent. Ass. 75: 639, 1967; Hayward et al., "Ca-A Cancer Journal For Clinicians". 13-21, April-May 1969; Cole et al., J. Dent. Res. Special Issue - Program and Abstracts 52: 246, 1973; Englander et al., J. Am. Dent. Ass. 78: 783, 1969; Carter, "Midwest Dentist," 43: 17, 1967; and Law, J. Am. Dent. Ass. 73: 835, 1966.
The only gelling agents specifically disclosed in these articles for use in neutral sodium fluoride gels are cellulose derivatives, either hydroxypropyl methyl cellulose or carboxymethyl cellulose.
Despite these disclosures in the literature of certain neutral sodium fluoride gels, the dental profession had continued to use the APF gels for topical fluoride application. This is surprising, since, from the standpoint of clinical efficacy, it is now believed that there is no significant difference between neutral sodium fluoride and APF.sup.(4), and yet there are some disadvantages to the use of the APF gel. For instance, APF has an acid etching potential for porcelain, polymer-glass composite material, and for metal bridge-work and orthodontic brackets. This could lead to staining, weakening, and reduction of polish. FNT (4) For review, see Ripa, Intl. Dent. J. 31, 105 (1981).
Up to now, most professional fluoride "gel" treatments have been carried out on pre-teenage children. On these patients, the acid etching potential of APF gel is not a significant problem because they have a low incidence of porcelain, composites, metal bridgework, etc. However, the dental profession has come to recognize that fluoride treatment would be beneficial to many more patients than pre-teenagers. For instance fluoride treatment to control and/or prevent caries is useful for those undergoing orthodontic treatment, children as well as adults. Because of improved preventive and treatment measures, more adults are retaining their natural teeth; therefore, coronal and root dental caries is becoming a significant health problem in the adult population.sup.(5). Adult patients suffering from gum disease such as gingivitis and periodontal disease would benefit from fluoride treatment to retard the formation of caries in the portions of the roots of teeth that are becoming exposed because of receding gum lines. Also, people who are handicapped, people with impaired salivary flow caused by head and neck radiation, and hemophiliacs can benefit from fluoride treatment to control dental caries. However, when fluoride gel treatment is extended to such patients, the acid etching potential of APF gel can become a significant concern. FNT (5) U.S. National Center for Health Statistics data, 1971-1974.
The present invention is based upon the discovery that a neutral sodium fluoride gel using a specified combination of thickeners or gelling agents is particularly well adapted for use in dental caries prevention and control.